1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the same.
2. Description of the Related Art
Recently, image pickup apparatuses (e.g., cameras) that use a solid-state image pickup device, for example, camcorders, digital still cameras, and monitoring cameras, have been required to be high-performance and small in the overall size. Accordingly, optical systems (e.g., photographing optical systems) used for these cameras, such as a zoom lens, are required to be small and have a wide field angle and high optical performance.
An example of a conventional small and wide-field-angle zoom lens is a negative lead type zoom lens that includes a plurality of lens units and in which the most object-side lens unit has a negative refractive power.
U.S. Pat. No. 5,386,320 discusses a three-unit negative lead type zoom lens that includes first to third lens units having negative, negative, and positive refractive powers in order from the object side to the image side and in which the first lens unit does not move during zooming and the first lens unit has a focusing function.
Japanese Patent Laid-Open No. 6-230281 discusses a three-unit negative lead type zoom lens in which the first lens unit consists of two lenses including a meniscus positive lens convex toward the object side.
U.S. Pat. No. 6,721,106 discusses a four-unit negative lead type zoom lens that includes first to fourth lens units having negative, negative, positive, and positive refractive powers in order from the object side to the image side and in which the first to third lens units move to zoom.
The above-described four-unit negative lead type zoom lens can be easily reduced in size and increased in field angle compared to the three-unit negative lead type zoom lenses.
However, since the entire lens system is asymmetrical, distortion tends to occur on the wide-angle side.
In addition, on the wide-angle side, it is difficult to secure a sufficient peripheral light quantity.